The present invention relates to an aircraft electronic system and particularly to a method and apparatus for configuring aircraft electronic circuitry.
An aircraft electronic system typically includes a flight management computer connected to a control display unit by means of which aircraft personnel interact with the computer through observation of screen displays and operation of input keys. The computer communicates with various sensors and control devices on the aircraft and plays a central role in coordination of aircraft operation. The flight management computer supplies computer aided data for automatically positioning the aircraft over a geographic location at a given speed, altitude and time, and also executes controlled maneuvers such as climb, descent, hold, reduced thrust take-off, and airfield approach to optimize speed and fuel consumption and minimize operational costs.
To accomplish various of these tasks, the flight management computer stores information in a navigation database. Navigation databases are usually customized for a particular airline and supply information specific to the routes taken by aircraft of that airline. Navigation databases are similar in content to aeronautical charts and approach/departure procedure plans and include a wide range of data regarding radio navigation, airport locations, airport runway configurations, airline routes, standard approaches, and standard departures. The flight management computer is suitably provided with a reprogrammable non-volatile memory (NVRAM) for storing mainly the aforementioned navigation database information. A database supplier provides the information on a tape cartridge fitting into a data loader unit which is connected to the flight management computer for transferring the navigation data from the tape cartridge to the NVRAM. Navigation databases are typically kept current by loading an updated version by tape cartridge every twenty-eight days.
Aircraft electronic systems are subject to extensive government agency regulation, and each aircraft component, such as the aforementioned flight management computer, must be certified and given a part number before installation or use in commercial aircraft. Many such components are designated with a single part number but have configuration options to suit the particular needs of different airlines. Each configuration option provides two choices, i.e., either the option is selected or not selected. To select between configuration options, the aircraft component includes a "configuration pin" for an option and this pin connects to aircraft wiring for receiving a discrete signal identifying the option choice. For example, an aircraft wire connected to a configuration pin corresponding to temperature display may be disconnected or left open to select centigrade temperature display values, and connected to ground to select Fahrenheit temperature display values. The present trend is to include more configuration options, and as the number of configuration options grows, so does the number of configuration pins for each aircraft component because a separate configuration pin is required for each pair of choices. The total number of configuration options for a given aircraft component is limited by the number of configuration pins which may be located thereon. Furthermore, additional configuration options increase the complexity of the aircraft wiring system because each configuration pin typically requires a dedicated aircraft wire to deliver the discrete signal.
The flight management computer is one example of an aircraft component having a single part number, but which may be configured according to the particular standards of the airline using the computer in its aircraft. Each airline configures all its flight management computers identically to avoid confusion and enable its pilots to change more easily between airplanes. Thus, a given airline might require the flight management computers in each aircraft to operate under CAA flight rules and also that temperature values be displayed in centigrade, while another airline might configure its flight management computers to operate under FAA flight rules and also to display temperature values in Fahrenheit. To select those options, the airline provides the suitable discrete aircraft wiring connected to configuration pins. The aircraft wiring must be certified, however, to insure that it can supply suitable values to the pins. If an airline then desires to change its configuration options, or if the aircraft is used by a different airline, it becomes necessary to rewire the aircraft in order to select the new options, and the process of rewiring an aircraft to select new configuration options must be authorized by the regulating authority and executed according to a set of instructions set forth in a "service bulletin". Each process of rewiring can, of course, be subject to error.
A flight management computer typically includes an input circuit card with a memory device. When the flight management computer is initialized at power-up with the airplane on the ground, the input circuit card scans the configuration pins and reads the discrete signal applied to each pin. The discrete values are then written into the memory device as configuration options data, and the flight management computer accesses the memory device to determine selected configuration options during operation. Configuration options data written into the memory device is lost when the flight management computer is turned off and the airplane is on the ground.
An aircraft crew may examine the status of each configuration option through a control display unit presenting menu screens on a CRT with each selectable menu item next to an associated input button. By depressing the appropriate input buttons, aircraft crew members can page through a series of menu displays and reach a display screen showing the status of each configuration option. The crew members cannot, however, change the option status.
Aircraft manufacturers wire and certify an aircraft, or fleet of aircraft, at the time of delivery according to the needs of the purchasing airline. Heretofore, the configuration options were seldom changed once the aircraft reached the hands of the purchasing airline and the aircraft seldom changed hands once delivered. However, many airlines now lease fleets of aircraft from leasing companies, and a single aircraft may be used by different airlines from year to year. Each time an aircraft is leased and placed in the hands of a new airline it may be necessary to rewire the aircraft in order to select the set of configuration options to be used, which, although intended to insure subsequent reliability, can, as stated, be subject to error. The rewiring procedure requires a service bulletin for certification, with the aircraft being taken out of service for the expensive reconfiguration. On the other hand, while it may be desirable to make reconfiguration convenient in order to reduce aircraft out of service time, reconfiguration should not be available to each aircraft crew since this might result in subsequent misinterpretation of data and unintended operation of the aircraft.